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1.
Complete Characterization of Phase and Amplitude of Bichromatic Extreme Ultraviolet Light
Primož Rebernik Ribič, Giovanni De Ninno, 2019, izvirni znanstveni članek

Opis: Intense, mutually coherent beams of multiharmonic extreme ultraviolet light can now be created using seeded free-electron lasers, and the phase difference between harmonics can be tuned with attosecond accuracy. However, the absolute value of the phase is generally not determined. We present a method for determining precisely the absolute phase relationship of a fundamental wavelength and its second harmonic, as well as the amplitude ratio. Only a few easily calculated theoretical parameters are required in addition to the experimental data.
Ključne besede: free-electron lasers, coherence, phase, attosecond
Objavljeno v RUNG: 12.01.2020; Ogledov: 2817; Prenosov: 0
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2.
Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser
Primož Rebernik Ribič, Giovanni De Ninno, 2019, izvirni znanstveni članek

Opis: X-ray free-electron lasers (FELs), which amplify light emitted by a relativistic electron beam, are extending nonlinear optical techniques to shorter wavelengths, adding element specificity by exciting and probing electronic transitions from core levels. These techniques would benefit tremendously from having a stable FEL source, generating spectrally pure and wavelength-tunable pulses. We show that such requirements can be met by operating the FEL in the so-called echo-enabled harmonic generation (EEHG) configuration. Here, two external conventional lasers are used to precisely tailor the longitudinal phase space of the electron beam before emission of X-rays. We demonstrate high-gain EEHG lasing producing stable, intense, nearly fully coherent pulses at wavelengths as short as 5.9 nm (~211 eV) at the FERMI FEL user facility. Low sensitivity to electron-beam imperfections and observation of stable, narrow-band, coherent emission down to 2.6 nm (~474 eV) make the technique a prime candidate for generating laser-like pulses in the X-ray spectral region, opening the door to multidimensional coherent spectroscopies at short wavelengths.
Ključne besede: free electron laser, coherence, x-rays
Objavljeno v RUNG: 07.05.2019; Ogledov: 3330; Prenosov: 0
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3.
The effect of lexical deficits on narrative disturbances in fluent aphasia
Sara Andreetta, Andrea Marini, 2015, izvirni znanstveni članek

Opis: Background: The label “fluent aphasia” applies to different aphasic syndromes char- acterised by fluent speech with difficulties in lexical retrieval and/or grammatical processing. Aims: This study aims at investigating microlinguistic and macrolinguistic skills in persons with fluent aphasia. We hypothesised that their lexical and syntactic (i.e., microlinguistic) difficulties would affect also their narrative (i.e., macrolinguistic) skills. Methods & Procedures: Growing evidence shows that traditional tests may not be sensitive enough to capture the patterns of the linguistic impairments observed in these persons. Therefore, we used a narrative task to elicit linguistic samples. Spontaneous speech was elicited through a picture description task. The narrative samples were analysed with a multilevel approach that allows clinicians to quantify their productivity levels as well as their lexical, grammatical, and narrative skills. The spontaneous speech produced by a group of 20 persons with fluent aphasia was compared to that of a group of 20 healthy participants. All participants with aphasia were in the phase of neurological stability. The two groups were matched for age and level of formal education. Outcomes & Results: Results showed that the lexical impairment observed in the group of participants with fluent aphasia hampered the ability to produce well-formed sentences that, in turn, lowered the levels of cohesion of their narrative samples. Furthermore, the reduced levels of lexical informativeness were found correlated also to the production of errors of global coherence. Conclusions: These findings support the hypothesis that in these patients, microlin- guistic difficulties might affect macrolinguistic processing. Furthermore, these results stress the importance of a multilevel approach to assess linguistic skills in patients with fluent aphasia, as it assesses both microlinguistic and macrolinguistic dimensions in parallel. Therefore, it allows linguists, psychologists, and clinicians to observe how the linguistic levels interact during natural language processing.
Ključne besede: neurolinguistics, aphasia, discourse analysis, coherence
Objavljeno v RUNG: 07.03.2016; Ogledov: 4481; Prenosov: 0
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